Colon cancer is one of the most common forms of cancer. Epidemiological evidence indicates that its genesis is environmental in nature and that diet may greatly influence its incidence. Dietary fiber has been implicated as protective whereas dietary fat may promote colon cancer. The effect of these two dietary components may be mediated through a common point - fecal bile acids. Evidence exists that fecal bile acids are tumor promoting agents. The proposed project is designed to investigate the effect of dietary fiber, derived from cereals and legumes, as well as fat on fecal bile acids (concentration and total excretion), and on the bile acid pool size. Four feeding trials will be conducted. In trials 1-3, rats will be fed a fiber-free diet or diets containing a fiber rich fraction. In trial 1 the fiber sources will be the brans of hard red spring, durum, and soft white wheat. In trial 2 the brans of oats, rye, barley and corn will be fed. In trial 3 fiber-rich fractions from pinto, navy, and kidney beans will be fed. In trial 4 the purified fibers cellulose and lignin as well as a purified soluble dietary fiber fraction and a purified insoluble dietary fiber fraction will be fed. In all 4 trials, each diet described will be fed at a low and high (5 vs. 20%) level of fat. After 5 weeks of feeding, fecal samples will be collected for 5 days and the pooled sample assayed for bile acids by high performance liquid chromatography after extraction with acidified ethanol and partial purification with C18 Sep-Paks. The animals will then be killed and the stomach, liver, small intestine, cecum, and colon taken, the bile acids extracted and assayed for bile acids to determine pool size. In addition, colonic 1 alpha-dehydroxylase activity will be determined using a radioassay. Results will be analyzed by two-way analysis of variance, with multiple comparisons to be made using the Bonferroni t-test.